1. Field of the Invention
The present invention relates to an air intake quantity controller for an engine which is mounted on a vehicle. More particularly, the present invention relates to the control of the quantity of auxiliary air that is supplied to such an engine through a bypass intake passage which bypasses a throttle valve.
2. Description of the Prior Art
A typical conventional air intake quantity controller for an engine is disclosed, for example, in Japanese Patent Post-Exam. Publication No. 64-4063 (1989). Hitherto, when a throttle valve that is associated with an engine shifts from an open state to a closed state, the quantity of intake air becomes insufficient, which results in the engine speed becoming lower than the idle speed or an increase in the content of harmful components (CO and HC) in exhaust gas, which are generated when the engine speed is reduced. In order to prevent a lowering of the engine speed and thereby reduce the content of harmful components in exhaust gas, the prior art is designed to increase the amount of auxiliary air passing through a bypass intake passage to cope with an engine decelerating condition from the time when an idle switch, for example, which detects whether or not the throttle valve is fully or substantially fully closed, i.e., whether or not it is in an idling position, changes from an "off" state to an "on" state. This control is effected by temporarily increasing the opening of an electrically-operated air control valve in excess of an ordinary basic control quantity, the control valve being provided in a bypass intake passage that bypasses the throttle valve.
The conventional air intake quantity controller for an engine suffers, however, from the following problems:
If the driver, for some reason, repeats an operation in which the accelerator pedal, which is in a released position, is slightly depressed and immediately released thereafter when the engine is in an idling condition, the throttle valve is slightly opened and then closed in response to the operation of the accelerator pedal and consequently the idle switch repeatedly changes from an "off" state to an "on" state. Since the opening of the air control valve is temporarily increased every time the idle switch changes, the increase in the opening of the air control valve is repeated. Thus, the quantity of auxiliary air that is sucked into the engine is repeatedly increased, causing the engine speed to rise to a level high above the idle speed.